It is standard practice in a machining operation when cutting, bending, stamping, or otherwise acting on a succession of like workpieces to set a stop against which the ends of the workpieces are pushed so that the machining operation takes place at a particular location relative to the workpiece end. When, for instance, cutting sections off channel (U-section) workpieces in a standard shear provided with a U-shaped passage into which the channel stock is pushed longitudinally, the stop is set at a longitudinal spacing from the blades that is equal to the length of workpiece section to be cut from the stock. A similar stop is provided in a bending apparatus to ensure that the bend is positioned at the desired distance from the workpiece edge.
In German patent document No. 1,502,774 filed with a claim to a French priority date of 29 Mar. 1963 and citing U.S. Pat. Nos. 666,449, 1,337,464, 2,520,495, 2,549,560, 2,821,252, and 2,933,966 a device is shown where the stop is carried on a pair of arms linked together so that the stop can move out of the way of the workpiece once the machine, here a shear, closes. The support arms are pivotally mounted and with time the support pivot pins become somewhat loose so that the position defined by the stop is no longer accurate. In addition such a system is fairly complex, having several parts that must be regularly serviced.
Such a stop is invariably adjustable in the longitudinal direction the workpiece is displaced in as it is fed to the working station of the machine, and is also normally vertically movable too. The stop must be deflectable out of the way so that, when the machine acts on the workpiece, it does not interfere with whatever operation is being carried out. For instance in a shear the stop must be vertically deflectable to allow the cut-off end of the workpiece to drop. Such a stop is also often provided with a switch which can be connected to the actuator for the machine it is used with so that the machine only operates when a workpiece is properly pressed against the stop.